1. Field of the Invention
The present invention relates in general to a method for controlling the temperature of a heat roller and an image forming apparatus based on the method. More specifically, the present invention relates to a method for controllably maintaining the temperature of a heat roller for fusing a toner image onto a sheet of printing paper at a certain level, and an image forming apparatus based on the method.
2. Description of the Related Art
An image forming apparatus operates to perform a designated data processing procedure on image data generated by the apparatus itself or inputted from an external device. Then, the image forming apparatus transmits the processed image data externally for printing onto a sheet of printing paper. Examples of image forming apparatuses include copiers, printers, scanners, fax machines, and multifunction apparatuses thereof.
The image forming apparatus exposes image data to a photosensitive object and forms an electrostatic latent image. Toner is applied to the electrostatic latent image using a developer. Thus, a toner image is developed. Consequently, the toner image is then transferred onto a sheet of printing paper. The toner image transferred onto the printing paper is fused by a fusing unit. Then, the image forming apparatus releases the sheet of paper externally, such as to a discharge tray.
The fusing unit of the image forming apparatus includes a press roller for pressing the printing paper after the toner image is transferred. A heat roller then heats the printing paper at a predetermined temperature. To heat the printing paper, the heat roller should be preheated. Otherwise, the toner image formed on the printing paper may not properly fuse onto the printing paper. Consequently, the toner image may become distorted.
To maintain the temperature of the heat roller at a certain level, the image forming apparatus measures the temperature of the heat roller every time a printing job is finished. If the temperature being measured is low, the image forming apparatus drives the heat roller during the pre-printing period to warm up the heat roller prior to printing.
However, in case another print job starts immediately after the previous printing job, the heat roller remains somewhat hot because of the residual heat from the previous printing job. Therefore, driving the heat roller during a pre-printing period is unnecessary. Moreover, a heat lamp is not necessary.
If the heat roller is not warmed during the pre-printing period, heat dissipates during the pre-printing period. In this case, the temperature of the heat roller during the printing job is noticeably decreased. As a result, the toner image formed on the printing paper is not properly fused onto the printing paper.
There have been a number of attempts to prevent the problem with the fusing process. One of them was to drive the heat roller anyway even when the temperature of the heat roller is high, but, this method only resulted in overheating of the heat roller, thus, causing the entire image forming apparatus to malfunction.
Accordingly, there is a need for an improved method of controlling the temperature of a heat roller to prevent image distortion during the fusing process.